150 Z.Bashir.N.Khan/Thermochimica Acta 276(1996)145-160 H0-(CH6-0-〈〉〉0-(CH6-oH+ (-0一(CH26-0〈 》-0-(CH26- Scheme 3.Reaction of BHHBP and isophthalic acid. polymer(referred to as the nascent polymer in the paper)showed perfect extinction at the clearing point under the polarizing microscope whereas the unpurified polymer showed some birefringent specks in the isotropic melt.Therefore purification of the polymer is important. 2.2.Differential scanning calorimetry (DSC) ments were oed using a Metler DSC 30 and C using an IBM or temperature and enthalpy response according to the melting points and heats of fusion of pure indium.The samples were encapsulated in hermetically sealed pans and the scans were conducted under a static air atmosphere. In order to find if the heating scans are dependent on the thermal history of the polymer,the same sample was used for all the experiments.Degradation was estab- lished not to be a problem providing the sample was not heated above about 150 C,as all features could be reproduced for a particular thermal history with the same sample For both heating and cooling experiments,a 20 mg sample and a 40 uL pan were used. 2.2.1.Heating scan of nascent and slowly crystallized polymer er). Fig.1b). 2.2.2.Heating scans of isothermally c vstallized polymer In ordr tondrtand the origin th miple eaks found in the heating scan shown in Fig la,an isothermally crystallized sampl was produced.Four
150 Z. Bashir, N. Khan/ Thermochimica Acta 276 (1996) 145-160 0 0 HO--(CH2)6--O~~~--O_(CH2)6__OH + CI CI O O (-- O-- (CH2)6-- O ~~~- O--(CH2)6-- O/~~ ) n Scheme 3. Reaction of BHHBP and isophthalic acid. polymer (referred to as the nascent polymer in the paper) showed perfect extinction at the clearing point under the polarizing microscope whereas the unpurified polymer showed some birefringent specks in the isotropic melt. Therefore purification of the polymer is important. 2.2. Differential scannin9 calorimetry (DSC) Calorimetric measurements were performed using a Mettler DSC 30 and TC 11 controller. This is a heat-flux type of DSC. Data storage and analysis were performed using an IBM microcomputer running Graph Ware TA-72 under QNX. The DSC cell was calibrated for temperature and enthalpy response according to the melting points and heats of fusion of pure indium. The samples were encapsulated in hermetically sealed pans and the scans were conducted under a static air atmosphere. In order to find if the heating scans are dependent on the thermal history of the polymer, the same sample was used for all the experiments. Degradation was established not to be a problem providing the sample was not heated above about 150°C, as all features could be reproduced for a particular thermal history with the same sample. For both heating and cooling experiments, a 20 mg sample and a 40/~L pan were used. 2.2.1. Heatin9 scan of nascent and slowly crystallized polymer The heating scan of the nascent polymer was recorded. Heat from 30°C ~ 150°C at 5°C min 1 (heating scan of nascent polymer, Fig. la). Cool from 150°C ~ 30°C at - 5°C min 1 (to form slowly-crystallized polymer). Heat from 30°C ~ 150°C at 5°C min - 1 (heating scan of slowly-crystallized polymer, Fig. lb). 2.2.2. Heatin9 scans of isothermally crystallized polymer In order to understand the origin of the multiple peaks found in the heating scan shown in Fig. la, an isothermally crystallized sample was produced. Four isothermal
Z.Bashir.N.Khan/Thermochimica Acta 276(1996)145-160 151 crystallization temperatures were tried (100C,105C,110C and 115C).The pro- cedure used for isothermal crystallization was as follows: Heat 30C-150C at 5C min(destroy thermal history of nascent polymer). Cool from 150C-100C (or 105C,110C.115C)at -5C min-1. Hold isothermal at 100C (or 105C,110C,115C)for 5h (isothermal crystalliza- tion). Ouench to -50C. Reheat-50C-150C at 5C min-(heating scan of isothermally crystallized polymer,.Fig1c-le以 2.2.3.Heating scans of quench-cooled polymer The quench-cooled sample was produced in order to measure the glass transition and compare its heating scan with that of the nascent polymer. Heat from -100C-150C at 5C min-1. Hold isothermal at 150C for 1 min n from DSC cel and immerse in liquid nitrogen(to produce quench- led s -100C and allow 10 min to equilib at I and n -100C for 10 min (heating scan of quench-cooled sample, Fig.10) 2.2.4.Coolin orde g sc mns and e ct of cooling rat her th ons could be resolved on melt was 001 he lowest possib scans were thus performed at cooling rates of 5,-0.7 3,and The following sequence was used for the first cooling rate: Cool from150°C+30°Cat-5°Cmin In the above sequence,the sample was heated very rapidly to the starting tempera- ture of 150C(for isotropization). For the very slow cooling scans (-0.7,-0.3 and -0.1C min),the following procedure was used in order to reduce the length of the experiment.Again,the sample was heated very rapidly to the starting temperature of 150C for isotropization,and was cooled in two stages as shown below. Cool from 150C-120C at-5C min-1(there are no transitions in this interval and a faster rate cuts time). Cool from 120C-70C at -0.7C min (or -0.3,-0.1C min). 2.3.Optical microscopy Optical observations were made with a Zeiss Axioplan polarizing microscope equipped with long working distance objectives.The samples were heated and cooled with a Linkam hot-stage and associated temperature controller.Very small powdered
Z. Bashir, N. K han/Thermochimica Acta 276 (1996) 145-160 151 crystallization temperatures were tried (100°C, 105°C, 110°C and 115°C). The procedure used for isothermal crystallization was as follows: Heat 30°C - 150°C at 5°C min- 1 (destroy thermal history of nascent polymer). Cool from 150°C ---, 100°C (or 105°C, 110°C, 115°C) at - 5°C min- 1. Hold isothermal at IO0°C (or 105°C, 110°C, 115°C) for 5h (isothermal crystallization). Quench to - 50°C. Reheat -50°C ---, 150°C at 5°C min 1 (heating scan of isothermally crystallized polymer, Fig. lc-le). 2.2.3. Heatin9 scans of quench-cooled polymer The quench-cooled sample was produced in order to measure the glass transition and compare its heating scan with that of the nascent polymer. Heat from - 100°C --, 150°C at 5°C min- 1. Hold isothermal at 150°C for 1 min. Remove pan from DSC cell and immerse in liquid nitrogen (to produce quenchcooled sample). Set DSC cell at - 100°C and allow 10 rain to equilibrate• Reinsert pan in DSC cell and hold isothermal at - 100°C for 10 min. Heat from - 100°C --, 150°C at 5°C min- 1 (heating scan of quench-cooled sample, Fig. lf). 2•2.4. Coolin9 scans and effect of coolin9 rate In order to check whether three exothermic transitions could be resolved on cooling, the isotropic melt was cooled at the lowest possible cooling rates attainable. DSC scans were thus performed at cooling rates of -5, -0.7, -0.3, and -0.1°C • --1 rain The following sequence was used for the first cooling rate: Cool from 150°C --, 30°C at - 5°C min- 1. In the above sequence, the sample was heated very rapidly to the starting temperature of 150°C (for isotropization). For the very slow cooling scans (-0.7, -0.3 and -0.1°C min 1), the following procedure was used in order to reduce the length of the experiment. Again, the sample was heated very rapidly to the starting temperature of 150°C for isotropization, and was cooled in two stages as shown below. Cool from 150°C--, 120°C at -5°C min-1 (there are no transitions in this interval and a faster rate cuts time). Cool from 120°C--.70°C at -0.7°C min 1 (or -0.3, -0.1°C min 1). 2.3. Optical microscopy Optical observations were made with a Zeiss Axioplan polarizing microscope equipped with long working distance objectives• The samples were heated and cooled with a Linkam hot-stage and associated temperature controller. Very small powdered