Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/3276
標題: Studies of Morphological Observations and Crystallization Mechanisms for Polyether-Polyester Segmented Block Copolymers with Amide Linkages
具醯胺鍵結之聚醚聚酯團聯共聚合物之形態觀察與結晶模式探討
作者: 紀志偉
Chi, Chih-Wei
關鍵字: negative birefringence;負光性雙折射;excluded mode;included mode;glass transition temperature;melting behavior;crystallization rate;morphology;confined effect;外排模式;內含模式;玻璃轉移溫度;熔融行為;結晶速率;形態;受限影響
出版社: 化學工程學系
摘要: 
Complicated crystallization and melting behavior has been observed in a series of polyether-polyester segmented block copolymers. The molecular weight of polyether segment is ca. 2000 g/mol. At polyether content below 40 wt %, polyether segment (i.e., soft segment) is non-crystallizable due to the blocking effect of crystallizable polyester segment (hard segment). The polyester component crystallizes as a typical spherulitic morphology with negative birefringence and linear boundary. We found that the inflection point method to determine glass transition temperature for polyether-polyesters is much reliable than the traditional method for Tg measurement. The compositional variation of glass transition for polyether-polyesters shows a similar trend to the prediction of thermodynamic theory for compatible polymer blends. This indicates that the incompatible pair of polyether and polyester segments becomes compatible after copolymerization. Unlike homopolyesters, the glass transition temperature of amorphous domains gradually decreases during crystallization from which an excluded mode for crystallization of polyester segments is suggested. Furthermore, we found that the broadness of glass transition temperature range increases with isothermal crystallization time. We suggest that the broadening behavior may be attributed to the crystallization-induced concentration gradient. After crystallization, the polyether component is excluded from polyester crystalline regions. Instead of forming macrosegregation, the excluded polyether segments are well mixed with amorphous polyester in-between polyester crystalline lamellae.
When polyether content increases to 50 wt %, the blocking effect on polyether segment diminishes so that polyether component becomes crystallizable. The polyether-polyester copolymers with dual crystallizable components give rise to a variety of particular morphology. Amorphous polyether-polyesters with well-mixed polyether and polyester segments is obtained after quench from the melt. Polyether component crystallizes from the amorphous state as sub-micrometer crystalline domains isolated by amorphous regions. As compared to homopolyether, the copolymerization of polyester with polyether leads to the depression in melting temperature and the decrease on crystallization rate due to the blocking and dilution effects. The melting temperature of polyether in copolymer increases with the increasing of crystallization temperature. This melting behavior is much different to that of homopolyether where the melting temperature is almost independent of crystallization temperature. We speculate that the chemical connection of polyether and polyester segments makes the low molecular weight polyether component act like a long chain polymer.
While polyester in high ether content copolymer is crystallized, polyester forms spherulite-like crystalline domains but without specific textures of spherulites such as Maltese cross and birefringence. Furthermore, a unique morphology was obtained. These crystalline domains are surrounded by amorphous region. This morphological texture results in a channel-like morphology observed under PLM and TEM. A corresponding schematic molecular model was proposed. Unlike homopolyester, the polyester crystalline lamellae grow randomly but not radially from the center of spherulite-like region. With the increase of crystallinity, the concentration of excluded polyether in the growth front of polyester lamellae gradually increases. The change in concentration profile continues until the concentration of polyester is too low for crystallization where amorphous regions remain as surrounding boundaries. For crystallization of polyether from the specific morphology, polyether component is more or less confined by the already crystallized polyester regions. The confined effect can be originated from space where polyether crystallizes either in-between lamellae or spherulite-like regions or from chemical connection where the mobility of polyether segments is limited by crystalline polyester segments. The melting behavior of polyether component indicates that the confined effect results in significant depression in melting temperature of polyether component. The confined effect also shows dramatic influences on the crystallization rate of polyether, in particular, at condition of high temperature crystallized polyester segments. Owing to the confined effect, the melting temperature is found to be independent of crystallization temperature.

本實驗探討一系列聚醚聚酯團聯共聚合物,聚對苯二甲酸乙二酯(poly(ethylene terephthalate), PET)與聚乙烯醚(poly(ethylene oxide), PEO)之共聚合物,其複雜的結晶與熔融行為,此聚醚團聯的分子量大約為2000g/mol,當聚醚含量小於40wt%時,由於結晶性聚酯團聯(硬段)的間隔作用,而導致聚醚團聯(軟段)無法結晶;在結晶形態方面,由聚酯團聯所形成的結晶呈現典型的球晶形態且具有負光性雙折射(negative birefringence)的特色。對於非結晶共聚合物的樣品,我們發現玻璃轉移溫度的測試方式以反曲點的方法所求得的聚醚聚酯團聯共聚合物玻璃轉移溫度比傳統的測試方法更為可信,不同聚醚含量之共聚合物皆呈現單一的玻璃轉化現象,表示聚醚團聯與聚酯團聯由於共聚合的效應有較佳的相容性,其玻璃轉移溫度(Tg)隨聚醚含量的增加而下降,有趣的是,此變化曲線與針對理想混合之高分子摻合系統依據熱力學理論所推導之Tg隨組成的變化情形相吻合,此現象可進一步的確認共聚合方式所引起的相容特性。
在結晶的過程中,共聚合物非結晶區的玻璃轉移溫度隨結晶度的上升而逐漸降低,因此推測聚酯團聯的結晶過程應為外排模式,而且,我們發現隨著等溫結晶時間的增加,玻璃轉移溫度的範圍變的寬廣,這個現象歸因於結晶時聚醚成份被聚酯的結晶區排除出來,使得聚醚團聯與非結晶的聚酯在聚酯的結晶層板間均勻混合,因而導致聚醚團聯於非結晶區的濃度分佈。
當共聚合物中聚醚含量增至50wt%時,聚酯團聯的間隔效應將逐漸降低,以致於聚醚團聯可以進行結晶,聚醚聚酯共聚合物因此具有雙結晶性,且將呈現多樣化的特殊形態。非晶態的聚醚聚酯從熔融態迅速降溫後聚醚與聚酯均勻混合,聚醚團聯從非晶態結晶成為次微米的結晶尺寸,且被非結晶區所隔離,與聚醚均聚合物的結晶與熔融行為作比較,由於間隔與稀釋作用,導致聚酯與聚醚的共聚合後熔點的大幅降低以及結晶速率的下降,在共聚合物中,聚醚的熔點隨結晶溫度的增加而升高,我們推測聚醚與聚酯團聯的化學鍵結將使得低分子量的聚醚團聯表現類似長鏈的高分子的結晶行為。
當聚酯在高聚醚含量的共聚合物中結晶,聚酯形成類似球晶的區域,但並沒有呈現特殊的球晶結構,例如馬爾它交叉(Maltese cross)與球晶光性,且這些結晶區被非結晶區所環繞,在PLM與TEM下觀察,形成類似渠道的形態,我們推論此共聚合物中聚酯的結晶層板從類似球晶區域的中心呈隨機但不是放射狀的成長,且隨著結晶度的增加,由於外排的聚醚濃度的逐漸增加,在聚酯結晶層板的前端成長將形成非結晶區的區域環繞於結晶邊界,此時聚醚成份或多或少被已結晶的聚酯區域所限制,限制的效應來自於聚酯結晶的空間侷限效應,如結晶層板之間與類似球晶的區域間,或來自於化學鍵結的影響,此時聚醚團聯的移動性將受到聚酯團聯結晶的限制,聚醚團聯的熔融行為受上述限制效應所影響,結果造成聚醚團聯熔點的降低,同樣的,限制效應也影響到聚醚的結晶速率,尤其在聚酯團聯高溫結晶條件下,聚醚的結晶速率明顯受到影響而趨於緩慢。
URI: http://hdl.handle.net/11455/3276
Appears in Collections:化學工程學系所

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