I Structure-Properties Correlation in Copolymers of Methyl ... - DRDO

Defence Science Journal, V 01 47, ~o 3, July I ~97, pp. 401-409 Q 1997, DESIDO~ ,

, ~

I Structure-Properties \ Methacrylate ,

Correlation & Alkyl

Seema Defence

Researc,h

&

DevelJpment

in Copolymers Methacrylates

of Methyl

Agarwal Establishment.

Gwalior-474

002.

and

Veena Indian

Institute

Choudhary of

&

Technology,

I.K. New

Varrna Delhi-110

016

ABSTRACT

I

The resul~ o~ a study on the copolymerisation of methyl methacrylate (MMA) with varying mol fractions of octyl m~thacrylate, decyl methacrylate (DMA), lauryl methacrylate (LMA) and stearyl methacrylate (SMA~ by free radical polymerisation using benzoyl peroxide as the initiator are presented. It was hnticipated that ~ncorporation of alkyl methacrylate (AMA) having a long alkyl side chain in poly(methyl methadrylate) (PMMA) backbone may lead to an improvement in the toughness I of the cast sh~ets. Such copolymers can be u~ed for low temperature applications in defence. I The glas.s transition temperature of the polymers determined using differential scanning calorimetry was found to decrease with increase in length 9f the alkyl side chain and the comonomer content. A significant increase in percent!lge elongation and decrease in tensile strength, modulus anQ . per cent transmittance was observed on incorporation of AMA in PMMA backbone. In the copolymers of SMA and MMA, significant opacity was observed. I

I.

INTRODUCTION

i

Varma and coworkersl-8 sation and thermaf behaviour (MMA)

with several vinyl

reported of methyl monomers.

plasticisation

due to the presence of long alkyl

copolymeri-

chain would

lead to an improvement

methacrylate

of the fast sheets without

The effect of

useful optical

alkyl groupt and structure of the side chain! on physico-met:hanical properties of cast acrylic sheets was als() studied6. I. t The

present

systematically in

alkyl

composition

st~dy

was

aimed

At ,

investigating

the effect of length qf the side chain

mcthacr}\late I

on

(AMA)

the

bnd

properties

Rcccivcd25 July 1996,rc:!viscd~8January1997

in toughness affecting

properties.

the

Such cast

sheets may be used for low temperature applications in defence. Several copolymer sheets were therefore prepared by copolymerising 0.05-0.25

mol

(OMA),

fractions

decyl

copolymer

meihacrylate

of

(SM~)

MMA

significantly

and mechanical

side

of

octyl

methacrylate (I.MA) I

with MMA.

and

methacrylate

(DMA), stearyl

lau~yl

methacrylate

The effect of I~ngth of the alkyl I 401

DEF SCI J, VOL 47, NO 3, JULY 1997

transmittance, mechanical properties and softening temperature was evaluated. 2

I.:X I.I~ It IM I.:NT A I.. D I~T A 11..S

2.1 M a terials Methyl methacrylate (MMA, Aldrich) was purified by washing with 10 per cent NaOH solution followed by water. MMA was left overnight over anhydrous Na2S04 and diJtilled under reduced pressure. OMA, DMA, LMA and SMA were synthesised in the laboratory by esterifying methacrylic acid with corresponding alcohol using p-toluene sulfonicl acid as catalyst. Benzoyl peroxide (BPO) was tecrystalli'sed from chloroform

solution.

I bath and the temperature 4

hr.

The

assembly

maintained

was

then

) at 15 °c for

removed ,

a~d

placed

in an air oven ~t 90 °c for 90 min and then at 120 °c fur ullutl,cr 90 mill. 011 tllc CUillplctiull uf polymerisation. tpe mold was cooled and solidified , I 3 acrylic sheets of 18 x 24 x 0.2 cm were taken out by p~ssing a stream of w~ter. I , I copolymer

Twenty taking

different

comonomers initial

sheets

mol

(OMA,

were

fractions

DMA,

or

voids.

by of

t

~MA

and SMA)

feed. All fabricated'sheets

bubbles

Ifepared

I (0.05-0.25)

in the

were free from air

sheets have been , designated as OMS, OMS, LMS and SMS, respec~ively. A. suffix indicating the mol per cent of .comonomers

These

taken in the initial

feed has been

, appended to the generic nam,e. For example,

a sheet

2.2 Preparation or Prepolymer Syrup To fabricate sheets, a prepolymer syrup was prepared by taking requisite quantities of MMA and comonomers in a round bottom flask fitted with

prepared by using 5 pr 25 mol per cent of OMA

a nitrogen inlet and a reflux condenser. Nitrogen gas was bubbled through the solution and then

are given

1 per cent (w/w) BPO was added. The temperature was then raised to 75 °C. When the extent of conversion was -15 per cent, the flask was

be,en

designated

respectively. designation

as

IOMS-5

or

in Table

I. ~~sidual

monomer

release agent. A polyvinyl chloride (PVC) gasket of 2 mm diameter was placed in between the plates which were held together by ~sing steel clamps. One side of the n1old was kept 9Pen for pouring the prepolymer syrup. 2.4 Fabrication

of Sheets 1 f About 100 ml of monomer-polymer syrupwas used for fabricating sheets, because it reduces the amount of heat to be dissipated, reduces tthe probability of trapped air bubbles, shrinkage and also lowers the initiation temperature. After filling the glass mold with the prepolymer syrup, the opening was closed using a metal plate and clamps. The filled mold was placed in a preheated water 402

content

Table I. Characteristics of:lkyl methacrylate copolymer sheets fabricated , Density at 28+0.1 °c (g/cm3) 1.176

or Mold

Two-toughened glass plates (21.5 x 29.0 cm2) were cleaned thoroughly and sprayed with a silicon

OMS-25,

The feed, cbmposition, sample and 'thickness of the fabricated sheets

removed and the reaction was arrested by quenchcooling the contents of the flask in ice water. 2.3 Preparation

has

OMS-5

.

OMS-IO OMS-15. OMS-20 OMS-25 , DM~-5 DMS-IO DMS-15 DMS-20 DMS-25

LMS-5 LMS-IO LMS-15 LMS-20 L~S-25 SMS-S' SMS-IO SMS-1S SMS-20

0.9510 0.9008 0.8528 0.8016 0.7523

1.88

0.9501 0.9012 0.8510 0.8001 0.7540

1.80

1.88 1.92 1.89 1.88

1.82 1.8~ 1.89; 1.89t

0.9517

1.79

0.901~ 0.851i 0.8031 0.7514

1.8b

0.9540 0.9011 0.8516

1.80

0.80231

1.88

2.05, 1.95' 1.65 2.70 1.94

1.80

1.8~ 1.89

1.157 1.131 1.111 1.102

2.65 2.90 2.05 2.45 , 2.50 \

1.162 1.'51 1.131 1.122 1.101

2.75 2.20

1.160 1.153 1.130 1.109 1.018

1.86 1.82

1.164

2.95 , 3.55 2.85 2.00 2.15

1.158 1.149 1.140 1.128

AGARWAL,

et al : STRUCTURE-PROPERTIES

I was

determined

sheets

by

with

exttacting

methanol

a small

fer

apparatus. ThF residual in all the coPflymers.

36

hf

portion

using

of

I

moJ1omer was -1.5 I

the

CORRELATION

recording

Soxhlet

function

per cent I I

which

IN COPOLYMERS

moduli

of temperature.

measure

solar

CHARACT~RISATION The

intrinsic

& TESTING I

viscosity

in

chloroform

was

I at 30 :t

Ubbelohde copolymer

suspension level. viscometer. The ( I samples in po\\\der form were used for

evaluati?g

T g using DSC t4chnique.

of

were obtained

sheets

polymer excess

°c

the\ polymers .

determined

samples

I

of

in

chloroform

by dropwise of

analyser

by dissolving and

~ddition

methanol.'

A

The powdered small

pifces

of th:is solution

having ;a 910 ~SC

module

1090

thermal

was used to

history

same,

samples

were

copolymers

heated

bnd this temperature

for 2 min. The samples pNere allowed

at a was to

cool and then DSC traces wdre recorded in a second I heating cycle. To characterise the glass transition I region, three chara~teristic temperatures were

T on Temperature at which deviation from the base line starts. It was obtained by extrapolating the base line and drawing tangent at the .steep portion of the curvet .

Tg

according tester

Post-transition temperature becomes straight; It extrapolation,' and I TempefatureJ

at the

at which the base line was obtained by

to ASTM

inflection

point

Dyna~ic

mm,

copolymer

measJrements

sheets 'werc carried

o~t using

df

mm)

of

the

of

the

P.olymcr

sirze of j

30

x ,10 x

of

I ahd 10 Hz and a

2 mm3

were

used

for

determined tensile

conditions. For I specimens (length section

12.5

mm,

were used. The edges of the

full

using

for

a fine sand paper.

testing

were:

Gauge

scale load = 500 kg, chart

of five

samples

were tested for each

composition.

4.

RESULTS All

& DISCUSSION

the fabricated

colourless

sheets were transparent

except SMS-20.

The intrinsic

which

composition.

(TI) of the copolymers

1.65-3.5

dl/g

I).

The TI

trend with copolymer

formed

for copolymers Isolated at low per cent), indicating that the

were of higher molecular

This can be attributed

to a reduction

at high conversion

due t() viscosity

effect),

weight

thereby

homopolymerisation9.

in

Table

to high

A gel effect

density

sheets was determined

summarised

per cent,

leading

has been reported The

weight.

in the termina-

( -98.5

copolymers.

15 per cent conversion

are

(Table

These values were higher than that of

the values obtained conversio'n 7 ( -12 polymers

and

was opaque.

viscosity

values showed no systematic

copolymers

frequencies

was

speed = 100 mm and cross head speed = 1 mm!min.

of 5 °C/ll1in,

mechanical

narrow

us~d

= 50 mm,

copolymer

dynarhic

ambient

were polished

conditions

length

I.thermal analyser model Mk II in the range 50-150 °~. A heati~g rate

Laboratories

sheets.

on an Instron

dumb bell-shaped

-2

specimens The

I at

width

thickness

molecular mechanical

the

were

0-638

model-1121

tion reaction

transitil!>n.

sample

properties

was in the range

noted:

TI

of

spectrophotometer

Properties

tensile

A minimum

powdered

in I?SC pan to 120 °c

heating rate of 10 °C/min maintained

the

The

165

To keep the thermal

.

3.1 J Mechanical

into

were used in each ~xperiment. th~

transmittance

was used to

used to measure transmittance of the sheets in the I wavelength range 300-800 nm.

tensile testing,

the transition temperatures. A sample size I of 5.9 :t 0.9 mg' a.nd a heating rate of 10 °C/min

all

pyranometer,

UV -visible

j the

evaluate

of

as a

using

precipitating

DuPont

and loss modulus)

The D and S alphatometer

is a miniaturised

Hitachi-330 3.

(storage

I.

above

in MMA of

the

and the results Density

of

the

decreased with increase in mol fraction I of the comonomers having long alkyl side.

403

DEF SCI J, VO~ 47, NO 3, JULY 1997 Table 2. Solar transmittance sheets

and turbidity

values for copolymer

The solar/ transmittance summarised

Sample designation

Solar transmittan(!e

Turbidity

solar transmitla?ce

('t)

ti on of

PMMA

0.91

0.052

increasing

OMS-2S

0.90 0.89 0.88 0.87 0.87

0.056 0.062 0.066 0.073 0.074:

DMS-5 DMS-IO DMS-15 DMS-20 DMS-25

0.88 0.88 0.87 0.86 0.85

0.071 0.070 0.076 0.080 0.086

LMS-5 LMS-IO LMS-15 LMS-20 LMS-25

0.88

0.84

0.071 0.077 0.081 0.083 0.097

SMS-S

0.86 0.82 0.70 0.25

0.081 0.107 0.189 0.737

OMS-S OMS-IO OMS-1S OMS-20

SMS-IO SMS-1S SMS-20

0.87 0.86 0.86

Table

80.0

3. Percent

15

LMS-5 LMS-IO LMS-15 LMS-20 LMS-25

78.2 79.5 74.0 78.0 78.0

82.5 82.5 79.0 78.2 82.0

80.0 73.0

fraction

when

mol

per

cent wl1ich

~nd LMA.

On

in the case of MMA-SMA

significant

"and

in

of comonomers, a , of copolymer sheets

in turbi~ity

decrease I

increase low of

in

in

mol

percentage

turbidity

fractions

'~MA

had

was reduced

70

was

of SMA

A copolymer

,when 20 mol per cent df SMA

having per

cent

to 25 per cent

was incorporated

in

poly(methyl fethacry,late) (PMMA) backbone. Decrease in transmittance on the addition of higher I mol fractions ofl SMA could be due to incompatibility

ofl

methacrylate),

which

chain.

PMMA

with

Ihds a non-polar

poly(stearyl alkyl

side

,

The percentage transmittance of the copolymer sheets at different wavelengt~ values for copolymer

83.2 8~.2 82.0 85.0 78.0

77.5

even

transmittance,

81.5 84.0 80.5 83.5 76.5

78.5 82.5 76.0 77.5 76.0

404

obs~rved

77.0

'1.0 77.0 70.0 71.5 71.0

OMS-20

mol

data are

decrease

on copolymerisa-

DMA

"were present in the backbone.

86.5

DMS-5 DMS-IO DMS-15 DMS-20 DMS-25

OMS-15

a

transmittance

85.5

80.2

the

OMA,

was seen. However,

83.0

OMS-25

OMS-IO

was obser~ed

with

increase

copolymers, "

lIght transmittance

67.0 75.0 72.0 74.0 67.5

OMS-5

MMA

marginal

~nd turbidity

in Table 12. A inarginaf

83.0

84.5

85.0

86.0

80.0

81.5

81.0

82.5

80.0

82.0

84.5

85.0 85.5 83.5 86.0 85.0

84.5 82.5 83.0 84.4

sheets at different

87.0

Was also measured

wavelength's

87.0

87.5

88.0 87.0 88.0 84.0 87.5 81.0

84.0

86.0

86.5

86.2

87.0

87.5

82.2

83.0

84.0

86.0

86.5

87.5

79.0

79.5

81.0

85.5 87.0 83.0 83.5 83.0

86.0

84.0

87.0 87.1 85.0 85.0

83.2

84.~

87.0 88.0 85.0 86.0 85.0

85.8

86.0 86.5 85.0 86.8 86.0

86.0 87.0 85.5 87.0 86.5

87.5 88.0 86.0 87.0 86.5

86.2 84.5 86.5 86.0

87.0 83.5

\

~

AGARWAL,

Table

I. values

4. Turbidity

ro~

et al : STRUCTURE-PROPERTIES

copolymer

sheets

at

different

CORRELATION

IN COPOLYMERS

Table 5. Glass transition

temperaturesjror

copolymer sheets

wavelengths

OMS-S OMS-IO OMS-IS OMS-20 OMS-2S

DMS-5 DMS-IO DMS-15 DMS-20 DMS-25

0.0788 I

0.0756

0.0694

0.1390 0.1173 0,1327 0~1180 0~1673

6.0978 0.08(> I 0.1093 0.085~ 0.1329

0.0802 0.07'40 0.0970 0.0767 9.122d

0..0740 0.0679 0.0908 0.0706 0.11 to

0.1341 0.1056 0.1491 p.1348 0.1452

0.0935 0.0815 0.1111 0.1017 0.1050

0.0837 0.0766

0.0773

0.1074

0.090'

LMS-S LMS-IO LMS-lS LMS-20 LMS-2S

0.1372

SMS-S

0.1380

SMS-IO

0.1760

SMS-lS

0.4201

SMS-20

Opaque

0.1 d68

0.087p 0.096~ 0.0828 0.0902

0.1267 0.1351

0..0902 9.1206 0.2529 I

0.098p 0.0922 0.0973

0.0702 0.0883 0.0798 0.0859

0.0842 0.0805 0.0859 0.0777 !>.0837

0.0778 0.0710 0.0798 0.0765 0.0805

0.090~ 0.1206 0.2529

0.0837 0.1072 0.2118

(Table 3). It was lowl at lower wavelength The

turbidity

increase

PMMA

0.1012

of

in

'the I

mol.

(Table

4).

The

showed

higher

copolymers

fraction J ;MMA:SMA

values

other copolymer

the

DMS-5 DMS-I0 DMSI-15 DMS-20 DMS-25 LMS~5 LMS-I0 LMS-20 LMS-25 SMS-5

97.2

(105)

83.3

(95.3)

76.9

(86.5)

58.1

(77.6)

56.6

(69.3)

97.0

(99.7)

80.0

(85.5)

71.0

(72.4)

62.0

(60.,0)

55.0

(48.9)

90.8

(98.9)

74.3

(84.4)

55.9

(57.0)

52.8

(45.0)

86.9

(-)

lEMPERATURE ~ C) 80 100

ro

with

120

DMS-5

l~

comonomer

copolymer

of turbidityl

sheets.

I

OMS-5 OMS-I0 OMS-15 OMS-20 OMS-25

(400 nm).

increased

of

I

114.8

sheets

as compared

to

1-