"กว่า......ก็...." and "พอ....ก็..." are both Thai conjunctive phrases that can be used to connect two clauses. However, there is a subtle difference in their meanings.
กว่า......ก็.... is used to express a contrast between two events or situations. The first clause describes a situation that has to be fulfilled before the second clause can happen.
For example:
กว่าฉันจะถึงบ้าน ฝนก็ตกแล้ว
gwàa chăn jà tĕung bâan · fŏn gâw dtòk láew
(By the time I got home, it was already raining.)
กว่าเธอจะยอมแต่งงานกับฉัน ฉันก็ต้องพิสูจน์ตัวเองให้เธอเห็น
gwàa ter jà yom dtàeng-ngaan gàp chăn · chăn gâw dtông pí-sòot dtuua eng hâi ter hĕn
(I have to prove myself to her before she will agree to marry me.)
พอ......ก็.... is used to express a sequence of events or situations. The first clause describes an event that happens, and the second clause describes the result of that event.
For example:
พอฉันถึงบ้าน ฝนก็ตก
paw chăn tĕung bâan · fŏn gâw dtòk
(As soon as I got home, it started raining.)
พอเธอแต่งงานกับฉัน เราก็ย้ายไปอยู่ด้วยกัน
paw ter dtàeng ngaan gàp chăn · rao gâw yáai bpai yòo dûuay gan
(Once she married me, we moved in together.)
In general, กว่า......ก็.... is used to emphasize the contrast between two events, while พอ......ก็.... is used to emphasize the sequence of events.
Here are some additional examples of how to use these phrases:
กว่าฉันจะเรียนจบ ป่านนี้พ่อแม่ฉันคงแก่แล้ว
(By the time I graduate, my parents will be old.)
พอฉันเรียนจบ ฉันก็จะหางานทำ
(Once I graduate, I will start looking for a job.)