臺灣博碩士論文加值系統

嵌段式聚氨基甲酸酯(segmeted polyurethane,PU)龐大的化學結構數目以
及內部特殊的微相形態,反映出多變的性質;但同時也複雜化了PU的形態,
結構和性質的關係.對此,文獻上一直都沒有肯定的結果,甚至出現許多矛
盾.本時驗藉由純硬質段PU的合成,結合之前時驗室合成相分離完全,且含
不同軟質段分子量及不同硬質段含量的PU,使實驗寒系統涵蓋了PU廣泛的
形態變化.由DSC直接測得的結果顯示,在純硬質相PU方面,發現MDI或TDI在
兩端的modelcompound Tg 會比BD在兩端的model compound 高,這可能是
因為BD在兩端的model compound其分子鍊末端猶如可活動的free chain
end 因此Tg會比較小.但此效應的影響於分子量逐漸加大的同時,會逐漸變
小.在軟質相玻璃轉變行為方面,本文由完全相分離的PU,發現PU單位質量
軟質段的△Cp(s)比軟質段prepolymer △Cp低,認為是因硬質相形態改變
引起△Cp(s)降低,並以此提出entropy restriction model 以解釋△Cp(
s)隨著硬質段含量增加成三階段式遞減和隨軟質段分子量降低而減小的現
象.另外,也指出過去文獻未考慮entropy 的限制效應,而直接採用比熱△
Cp變化量,來討論PU的相分璃程度是個嚴重錯誤.在硬質段玻離轉變行為方
面,本文直接且肯定的以DSC偵測到相分離完全之PU硬質段Tgh,並且發現
Tgh在軟質段分子量較低時,嚴重受軟質段分子量的影響,而在此低軟質段
分子量時,只要當硬質段分子量在3500以下,硬質段分子量亦會嚴重影響
Tgh.對於這種現象,本文認為是因為PU在軟,硬質鍊段均短時,其界面得完
整性會下降,而使硬質段末端有較大的移動性,因此使Tgh 降低.另外,也發
現硬質段會因兩相界面邊界的restriction效應,限制其鍊段自由度而導至
硬質段△Cp降低,此結果再次驗證entropy restriction model 對△Cp值
的影響.

The morphological effect on the soft segment thermal
transition of a series of Toluylene diisocyaanate (TDI) based
cis-polybutadiene (cis-PB) polyurethanes was studied by
differential scanning calorimetry(DSC).Number average molecular
of the soft segments ranged from 1000 to 4200.The hard segment
content ranged from 20% to 70%.For the cis-polybutadiene soft
segment,thermal transition behaviors of the glass transition
temperature(Tg),the breadth of the glass transition
temperature(△B),and the specific heat capacity(△Cp)were
investigated.Expermental results indicated that increased in Tg
and△B corrresponded to a decreased in the soft segment
molecular weight are attributed to decrease in free volume and
mobility due to bonding in soft segments to the rigid urethane
blocks.In each series of polyurethanes with a constant soft
segment molecular weight,both Tg and △B remain constant as
hard segment content increased from 20% to 70%,indicating the
phase seperation between the soft and hard segment is completed
even down to the interfacial region.By the results of△Cps,we
proposed the entropy restriction model to explain why the △
Cps can be decreased 50%,since the hard segment content
increased from 20% to 70%.And the entropy restriction model also
can explain why the higher molecular weight soft segment PU
samples'' △Cps are higher than low molecular weight PU samples.
After first run,all samples stayed 5 min at 180℃,than
quenched from 180℃ to -140℃ by the rate 320℃/min.Than we can
start second run ,and we can find the hard segment glass
transition temperature(Tgh). In these results,we can find that
if the hard segment molecular weight are the same,the Tg of
model compounds are lower than PU samples.these are due to all
mpdel compounds'' chain end are freedom and random distribution,
but the PU samples'' chain end are binded by the rigid and hard
interface.And we also can find in the same hard segment
molecular weight,if model compounds'' chain end group is -OH,
their Tg were lower than TDI or MDI ones.This is because the -OH
chain ends are like the free chain end.Thus their mobility are
higher and caused lower Tg.